Extreme hyponatraemia due to primary polydipsia and quetiapine-induced SIAD.

The combination of primary polydipsia and SIAD can lead to a life-threatening, extreme hyponatraemia. SIAD is an uncommon side effect of second-generation anti-psychotics. Serum sodium should be monitored in patients with primary polydipsia when commencing or adjusting psychotropic medications. Symptomatic hyponatraemia is a medical emergency that requires treatment with boluses of hypertonic 3% saline. A serum sodium of less than 105 mmol/L is associated with an increased risk of osmotic demyelination syndrome, therefore the correction should not exceed 8 mmol/L over 24 h.